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CAPS Member Bios
Philip R. Christensen, Arizona State University (Co-Chair)
Christopher H. House, The Pennsylvania State University (Co-Chair)
Sushil K. Atreya, University of Michigan
Richard P. Binzel, Massachusetts Institute of Technology
Ronald Breaker, Yale University
John Clarke, Boston University
Geoffery Collins, Wheaton College
Bethany L. Ehlmann, California Institute of Technology
Pascale Ehrenfreund, George Washington University
Kevin P. Hand, Jet Propulsion Laboratory
Sarah M. Hörst, Johns Hopkins University
James F. Kasting, Pennsylvania State University
Stephen Mackwell, Lunar and Planetary Institute
William B. McKinnon, Washington University, Saint Louis
Norman Pace, University of Colorado Boulder
Gary Ruvkun, NAS, IOM Harvard Medical School
Mark P. Saunders, Independent Consultant
David J. Stevenson, California Institute of Technology
Sarah T. Stewart, University of California, Davis
Elizabeth P. Turtle, Johns Hopkins University

PHILIP R. CHRISTENSEN is a Regents Professor and the Ed and Helen Korrick Professor in the School of Earth and Space Exploration at Arizona State University. His research interests focus on the composition, processes, and physical properties of Mars, Earth, and other planetary surfaces. Dr. Christensen uses spectroscopy, radiometry, field observations, and numerical modeling to study the geology and history of planets and moons. A major facet of his research is the design and development of spacecraft instruments, and he has built five science instruments that have flown on NASA’s Mars Observer, Mars Global Surveyor, Mars Odyssey, and the Mars Exploration Rover missions. Over the past decade he has studied urban environments and growth worldwide using satellite data and has developed an extensive K-12 education and outreach program to bring the excitement of science and exploration into the classroom. Dr. Christensen was awarded NASA’s Exceptional Scientific Achievement Medal in 2003, NASA’s Public Service Medal in 2005, and the G.K. Gilbert Award of the Geological Society of America in 2008. He is a fellow of the American Geophysical Union and the Geological Society of America. He received his Ph.D. in geophysics and space physics from the University of California, Los Angeles. Dr. Christensen has previously served as a member of the NRC Committee on Planetary and Lunar Exploration and as chair of the Planetary Science Decadal Survey’s Mars Panel.

CHRISTOPHER H. HOUSE is a professor of geosciences at the Pennsylvania State University. He is also director of the Penn State Astrobiology Research Center, director of the Pennsylvania Space Grant Consortium, and holds a faculty appointment in the Huck Institute for the Life Sciences at Penn State. His research interests focus on microbial diversity and cultivation, microbial paleontology, molecular evolution and genomics, astrobiology, and geomicrobiology. Dr. House is a past member of the Planetary Science Subcommittee of the NASA Advisory Council and the Scientific Ocean Drilling Vessel Program Advisory Committee; an Ocean Drilling Program Distinguished Lecturer; a participant in the Beckman Chinese-American Frontiers of Science Symposium; and is an editor of the journal Geobiology. Previously, Dr. House was an associate professor at the Pennsylvania State University. He earned his B.S. in biochemistry and cell biology from the University of California, San Diego and his Ph.D. in geology from the University of California, Los Angeles.

SUSHIL K. ATREYA is professor of atmospheric and space science at the University of Michigan. His current research interests include composition, chemistry, structure, and the origin and evolution of planetary and satellite atmospheres, particularly the giant planets, Titan, Mars, and Venus, and the formation of solar systems. Dr. Atreya is at present a member of the science teams of Cassini-Huygens, Mars Science Laboratory, Juno-Jupiter Polar Orbiter, Venus Express, and the Mars Express missions. He has received the NASA Award for exceptional scientific contributions to the Voyager missions to the giant planets (1981), the NASA Group Achievement Award for outstanding scientific contributions with the Voyager Ultraviolet Spectrometer (1981, 1986, 1990), and NASA group achievement awards for outstanding scientific contributions with the Galileo Probe mass spectrometer and outstanding contributions to the Galileo Project at Jupiter (1996). He is a fellow of the American Association for the Advancement of Science, a member of the International Academy of Astronautics, and a Distinguished Visiting Scientist at the Jet Propulsion Laboratory. He is the author of Atmospheres and Ionospheres of the Outer Planets and Their Satellites and editor of Origin and Evolution of Planetary and Satellite Atmospheres and three other books. He has served as a co-chair of the Venus Exploration Analysis Group (VEXAG) and as a member of the Steering Committee of the Outer Planets Assessment Group (OPAG). Dr. Atreya has served three 1-year terms on the NRC’s Panel on Space Sciences of the Policy and Global Affairs Division’s Associateship Program and has also served on the Committee on the Assessment of Solar System Exploration.

RICHARD P. BINZEL is a professor of planetary sciences, a Margaret MacVicar Faculty Fellow, and past chair of the Program in Planetary Science at the Massachusetts Institute of Technology. Dr. Binzel’s research interests include the collisional evolution of asteroids, planetary astronomy, and the physical parameters and surface features of the Pluto-Charon system. Dr. Binzel has conducted astronomical studies to investigate the compositional properties of asteroids passing near the Earth. He has also conducted intensive investigations of the distinct mineral absorption bands in the spectra of asteroids. He has earned a B.A. in physics at Macalester College and a M.A. and Ph.D. in Astronomy at the University of Texas, Austin. Dr. Binzel’s NRC service includes a term as a member of the Committee on Planetary and Lunar Exploration as well as chair of the Panel on Solar System Exploration for the Committee on Priorities for Space Science Enabled by Nuclear Power and Propulsion.

RONALD BREAKER (NAS) is the chair and Henry Ford II Professor of the Department of Molecular, Cellular and Developmental Biology at Yale University. He is jointly appointed as a professor in the Department of Molecular Biophysics and Biochemistry, and is an Investigator with the Howard Hughes Medical Institute. His graduate studies with Dr. Peter Gilham at Purdue University focused on the synthesis of RNA and the catalytic properties of nucleic acids. As a postdoctoral researcher with Dr. Gerald Joyce at The Scripps Research Institute, Dr. Breaker pioneered a variety of in vitro evolution strategies to isolate novel RNA enzymes and was the first to discover catalytic DNAs or “deoxyribozymes” using this technology. Since establishing his laboratory at Yale in 1995, Dr. Breaker has continued to conduct research on the advanced functions of nucleic acids, including ribozyme reaction mechanisms, molecular switch technology, next-generation biosensors, and catalytic DNA engineering. Most recently, his laboratory has established the first proofs that metabolites are directly bound by messenger RNA elements called riboswitches. Dr. Breaker’s research findings have been published in more than 100 scientific papers, book chapters, and patent applications, and his research has been funded by grants from the NIH, NSF, DARPA, the Hereditary Disease Foundation, and from several biotechnology and pharmaceutical companies. He is the recipient of fellowships from the Arnold and Mabel Beckman Foundation, the David and Lucile Packard Foundation, and the Hellman Family Trust. In recognition of his research accomplishments at Yale, Dr. Breaker received the Arthur Greer Memorial Prize (1997), the Eli Lilly Award in Microbiology (2005) and the Molecular Biology Award from the U.S. National Academy of Sciences (2006). Dr. Breaker has cofounded two biotechnology companies and is a scientific advisor for industry and for various government agencies. He serves on the editorial board for the scientific journals RNA Biology, RNA, Interdisciplinary Reviews: RNA, and Chemistry & Biology. He was elected to the NAS in 2013. He earned his Ph.D. in biochemistry from Purdue University. He was a member of the Committee on Astrobiology and Planetary Science.

JOHN CLARKE is a professor of astronomy at Boston University. His main research interests are in planetary atmospheres, their auroral and airglow emission, and ultraviolet space instrumentation. Prior to joining the faculty at Boston University, he worked at space science labs at the University of California at Berkeley, NASA’s Marshall and Goddard space flight centers, and the University of Michigan. Dr. Clarke served as the deputy project scientist for the HST project over 1984-1987, was a science team member on the Wide Field and Planetary Camera 2 project, and has participated in the flight of six sounding rocket experiments. He is presently PI for the Venus Spectral Rocket sounding rocket project, and a co-investigator on several space missions, including the Imaging Ultraviolet Spectograph (IUVS) instrument on the Mars Atmosphere and Volative EvolutioN (MAVEN) mission, the PHEBUS experiment (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) on the European Space Agency’s Bepi-Colombo mission to Mercury, and the ultraviolet imaging spectrograph instrument on NASA’s Juno Jupiter orbiter. Dr. Clarke received his Ph.D. in physics from the Johns Hopkins University. He was a member of the Giant Planets Panel of the Academies’ 2011 Planetary Science Decadal Survey.

GEOFFREY COLLINS is associate professor of geology in the Department of Physics and Astronomy at Wheaton College. In planetary science, his primary focus is on the geological features and geophysical processes of satellites in the outer solar system, including Ganymede and Europa at Jupiter and Enceladus, Dione, and Titan at Saturn. Beyond this focus, his research extends to geophysical phenomena on Venus, Triton, and Pluto. His contribution to the planetary science community includes membership on the science definition team for the Jupiter System Observer and NASA’s Outer Planet Assessment Group, as well as collaboration on the Galileo Image Team. Dr. Collins has served as principal or co-investigator for several research grants and has been awarded a Geophysical Research Letters Editor’s Citation for Excellence in Refereeing and the Brown Sigma Xi Research Prize. He received a B.A. from Carleton College and a Sc.M. and a Ph.D. from Brown University. He has previously served as vice chair of the NRC’s Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System.

BETHANY EHLMANN is an assistant professor of planetary science at Caltech and a research scientist at the Jet Propulsion Laboratory. Dr. Ehlmann’s research interests focus on planetary surface processes, infrared spectroscopy, the evolution of Mars, and chemical weathering and hydrothermal alteration throughout the solar system, among others. Previously, Dr. Ehlmann was a European Union Marie Curie Fellow and a collaborator on the Mars Exploration rovers during their primary and first extended missions. She is presently a co-investigator for the Compact Reconnaissance Imaging Spectrometer for Mars, Participating Scientist on the Mars Science Laboratory mission, Co-I on the Mars-2020 rover Mastcam-Z and SHERLOC instruments, and an affiliate of the Dawn science team. She is a recipient of American Geophysical Union’s Macelwane medal, Committee on Space Research’s Zeldovich medal, the Mineralogical Society of America, Distinguished Lecturer award as well as NASA Group Achievement Awards. She earned her Ph.D. in geological sciences from Brown University.

PASCALE EHRENFREUND is the chair of the German Aerospace Center (DLR) Executive Board. Dr. Ehrenfreund is also a research professor at the Space Policy Institute at George Washington University’s Elliott School of International Affairs. She was the president of the Austrian Science Fund (2013-2015). Her research expertise includes the investigation of organic matter in the interstellar medium and in solar system bodies, including planetary surfaces, comets, and meteorites as well as instrument development for life and organic detection on Mars; For two decades she contributed as Principal Investigator, Co-Investigator and Teamleader to ESA and NASA astronomy and planetary missions as well as experiments in low Earth orbit and on the International Space Station. She is Lead Investigator of the NASA Astrobiology Institute (Node Wisconsin) since 2008. She authored and co-authored more than 300 publications (Citation Index: H=59) and edited 12 books. Since 2010 she chairs the Panel on Exploration (PEX) of the Committee on Space Research (COSPAR). She holds a Ph.D. in astrophysics from the University Paris VII/University Vienna. She is full member of the International Academy of Astronautics (IAA) and served as a member of the Steering Group of the Academies’ 2011 Planetary Science Decadal Survey and the Academies committee on Human Spaceflight.

KEVIN P. HAND is the deputy chief scientist of solar system exploration at the Jet Propulsion Laboratory (JPL). He works on numerical modeling, laboratory experiments, and instrument development to advance our understanding of the physics and chemistry of ice-covered ocean moons in the outer solar system. His research interests include electromagnetic field interactions at icy worlds, radiolytic chemistry and implications for astrobiology, and spectroscopic biosignatures, among others. In his role as deputy chief scientist for solar system exploration Kevin helps guide JPL’s future for the robotic exploration of our solar system. He helps design and determines the missions that will best address the key science questions pertaining to the origin and evolution of planets in our solar system. He has worked closely with NASA Headquarters and educated members of congress about the value of solar system exploration. Previously, Dr. Hand was a scientist for the planetary ices group at JPL and was a visiting research fellow at Princeton University in the Department of Astrophysical Sciences. He is a recipient of the National Geographic Society Emerging Explorer Award and the Lew Allen Award for Excellence. He earned his Ph.D. in geological and environmental sciences from Stanford University.

SARAH M. HÖRST is an assistant professor at John Hopkins University in the Department of Earth and Planetary Sciences. Her primary research interest is atmospheric chemistry, particularly the complex organic chemistry occurring in the atmosphere or on the surface of bodies in the solar system. Previously, Dr. Hörst was a NSF Astronomy and Astrophysics Postdoctoral Fellow at the University of Colorado. She is a recipient of the Gerard P. Kuiper Memorial Award from the Lunar and Planetary Laboratory at the University of Arizona. She earned her Ph.D. in planetary science from the University of Arizona.

JAMES F. KASTING is Evan Pugh Professor at Pennsylvania State University. He research interests include atmospheric evolution, planetary atmospheres and paleoclimates. Before coming to Penn State University in 1988, he spent two years at the National Center for Atmospheric Research in Boulder, Colorado and seven years in the Space Science Division at NASA-Ames Research Center. He is a fellow of the American Association for the Advancement of Science, the International Society for the Study of the Origin of Life and the American Geophysical Union. He has published dozens of papers and two books, The Earth System (Prentice Hall 2009) and How to Find a Habitable Planet (Princeton University Press 2010). He is the recipient of the 2016 Stanley Miller Medal, also known as the NAS Award in Early Earth and Life Sciences. He earned his A.B. in chemistry and physics from Harvard University, and his M.S. in physics and atmospheric science from the University of Michigan where he also earned his Ph.D. in atmospheric science. He has served on the Academies’ Committee for US-USSR Workshop on Planetary Sciences (1988-1989) and the Panel to Review Terrestrial Planet Finder Science Goals (2004).


STEPHEN MACKWELL is the director of the Lunar and Planetary Institute in Houston, Texas. He is adjunct professor of Earth Science at Rice University. Prior to his current appointment, Dr. Mackwell served as the director of the Bayerisches Geoinstitut at the University of Bayreuth, Germany. Dr. Mackwell has served as program director for geophysics, Division of Earth Sciences, National Science Foundation (NSF; 1993-1994); as member, group chief, and panel chair of the review panel for NASA’s Planetary Geology and Geophysics Program; as expert reviewer for the Department of Energy’s Geosciences Research Program (1993); and as expert consultant for the Division of Earth Sciences, National Science Foundation (1995). Dr. Mackwell conducts laboratory-based research into the physical, chemical, and mechanical properties of geological materials under conditions relevant to the mantle and crust of Earth and other terrestrial planets. He served on the NRC Committee on New Opportunities in Solar System Exploration, the NRC Committee to Review Near-Earth-Object Surveys and Hazard Mitigation Strategies, the NRC Committee on the Planetary Science Decadal Survey, the NRC Planning Committee on Lessons Learned in Decadal Planning in Space: A Workshop, and the NRC Committee on Review of the Draft 2014 Science Mission Directorate Science Plan. He currently serves on the NRC Committee on Astrobiology and Planetary Science.

WILLIAM B. MCKINNON is professor of Earth and planetary sciences at Washington University, Saint Louis. He also serves as fellow of the McDonnell Center for the Space Sciences. Dr. McKinnon’s research interests include the structure, origin, evolution, geology, and bombardment history of outer planet satellites and dwarf planets; and impact mechanics on rocky and icy bodies. Previously, Dr. McKinnon was a visiting scientist at the South West Research Institute in Boulder, Colorado. Dr. McKinnon has received two group achievement awards from NASA, asteroid 9526 Billmckinnon is named for him, and in 2014 he received the G.K. Gilbert Award from the Planetary Geology Division of the Geological Society of America. He earned his Ph.D. in planetary science and geophysics from the California Institute of Technology. He served as a member of the Academies Committee on Priorities for Space Science Enabled by Nuclear Power and Propulsion: A Vision for Beyond 2015 and the Committee on Planetary and Lunar Exploration.

NORMAN PACE (NAS) is a professor at the University of Colorado in the Department of Molecular, Cellular, and Developmental Biology. Dr. Pace is an internationally recognized expert in nucleic acids and associated enzymes. His studies of ribosomal RNA structures have set new standards for the definition of phylogenetic relationships among organisms. His research interests include RNA enzymes, RNA processing, macromolecular structure, molecular evolution, and microbial ecology. Dr. Pace formerly served as a member of the Board on Scientific Counselors for the National Center for Biotechnology Information, National Library of Medicine. He is a fellow of the American Association for the Advancement of Science and the American Academy of Microbiology. He earned his Ph.D. in microbiology from the University of Illinois at Urbana Champaign. In addition, he has served on academies’ committees including the Committee on the Origins and Evolution of Life in the Universe, the Committee for a Review of Programs to Determine the Extent of Life in the Universe, and the Steering Group for the Workshop on Size Limits of Very Small Microorganisms.


GARY RUVKUN (NAS, IOM) is a professor of genetics at Harvard Medical School and Massachusetts General Hospital in Boston MA. Dr. Ruvkun’s laboratory identified the first microRNA that is conserved across animal phylogeny including humans. Thousands of microRNAs have subsequently been discovered. Dr. Ruvkun has also explored how bacterial attacks on animals are surveilled and countermeasures are deployed. Using comparative genomics, Dr. Ruvkun’s laboratory has been exploring the few hundred genes that are universal to all known life on Earth, inherited from a common ancestor over the past 3-4 billion years. Meteoritic exchange between Earth and Mars may have innoculated both planets with related ancestral organisms, allowing the sophisticated DNA technology of genomics to be marshalled to the detection of life on Mars. To this end, Ruvkun is collaborating with Chris Carr and Maria Zuber at MIT on a NASA MATISSE project to engineer a DNA sequencing instrument that will be deployed to other planets to search for life that is ancestrally related to life on Earth. Dr. Ruvkun is a graduate of UC Berkeley (A.B. Biophysics) and Harvard University (Ph.D. Biophysics). Dr. Ruvkun’s honors and awards include the National Academy of Sciences, the Albert Lasker Award for Basic Medical Research (with Victor Ambros and David Baulcombe), the Dan David Prize for Aging research (with Cynthia Kenyon), the Wolf Prize (with Victor Ambros), the Gruber Prize (with Victor Ambros and David Baulcombe), and the Breakthrough Prize in Life Sciences. Dr. Ruvkun is a graduate of UC Berkeley (A.B. Biophysics) and Harvard University (Ph.D. Biophysics). He has served on the NRC’s KFoS Five-Year Review Committee, the Organizing Committee for the Eleventh Annual Symposium on Frontiers of Science, and the Committee on the Origins and Evolution of Life

CRISTINA TAKACS-VESBACH is an associate professor in the Department of Biology at the University of New Mexico. Dr. Takacs-Vesbach conducted her graduate work in microbial ecology and performed research on the factors affecting bacterioplankton distribution and productivity in the Dry Valley Lakes of Antarctica. Her post-doctoral work focused on the microbial phylogenetic and physiological diversity of hydrothermal springs. Dr. Takacs-Vesbach is the recipient of the outstanding doctoral student award of the Montana State University Foundation, the John Wright Award for Limnology, and the Gary Lynch Award from the MSU Department of Biology. Her current research focuses on molecular microbial ecology—especially microbial diversity and productivity in extreme environments. Her NRC experience includes service on Committee on Preventing the Forward Contamination of Mars, the Planning Committee for the International Polar Year, and the Committee on the Origins and Evolution of Life.

MARK P. SAUNDERS is an independent consultant. Since retiring from NASA in December 2008, he has been consulting to various NASA offices providing program/project management and systems engineering expertise. This has included support to the Office of Chief Engineer, the Office of Independent Program and Cost Evaluation, the Mars Program and the Science Office for Mission Assessments (at Langley Research Center). He has participated in the rewriting of NASA’s policy on program/project management; advised and supported the Agency’s independent program/project review process; and has supported the review of various programs and projects. At NASA Headquarters he served as director of the independent program assessment office, where he was responsible for enabling the independent review of the Agency’s programs and projects at life cycle milestones to ensure the highest probability of mission success. At NASA’s Langley Research Center he was initially the deputy director and then the director, Space Access and Exploration Program Office (SAEPO) and had the responsibility for planning, directing and coordinating the center's research, technology, and flight programs for advanced aerospace transportation and human/robotic exploration systems. Prior to this he was the manager of Exploration Programs and led all LaRC space exploration research and development activities supporting the agency’s Aerospace Technology (AST), Human Exploration and Development of Space (HEDS) and Space Science Enterprises (SSE). At the office of space science he served as program manager for the Discovery Program, and at the space station freedom program operations he served as special assistant to the deputy director. He received the Presidential Meritorious Rank Award in 2008, Outstanding Performance awards: 1982, 1994- 2008 and the NASA Outstanding Leadership Medals in 1998, 2004, 2006. He earned his B.A. at the Georgia Institute of Technology in industrial engineering. He was a member of the Academies’ Committee on the Review of MEPAG Report on Planetary Protection for Mars Special Regions.

DAVID J. STEVENSON (NAS) is the Marvin L. Goldberger Professor of Planetary Science at the California Institute of Technology (Caltech). Dr. Stevenson’s research focus is theoretical planetary science, including Earth, large moons, and planets in other solar systems. His research applies condensed matter physics and fluid dynamics to data from space missions, including NASA’s Galileo, Cassini and Juno missions. Previously, Dr. Stevenson served as chairman of the Geological and Planetary Sciences Division and as chairman of the faculty at Caltech. Dr. Stevenson was elected as a foreign associate of the National Academies in 2004. He is also a fellow of the American Geophysical Union (AGU), the American Advancement for the Association of Science, and the Royal Society (London). He is a winner of the Division of Planetary Science (American Astronomical Society) Urey Prize, AGU’s Whipple Award and the Hess Medal. Dr. Stevenson received his Ph.D. in theoretical physics from Cornell University. He is a member of the National Academy of Sciences and served on the Astro2010 Panel on Planetary Systems and Star Formation, the Steering Committee of the Planetary Science Decadal Survey (2011) and the Solar System Exploration Panel of the Committee on Priorities for Space Science Enabled by Nuclear Power and Propulsion.

SARAH T. STEWART is a professor at the University of California, Davis in the Department of Earth and Planetary Sciences. She is also a visiting professor at Harvard University. Her research interests include the formation and evolution of planetary bodies with a focus on collisional processes. Previously, Dr. Stewart was a professor of Earth and Planetary Sciences at Harvard University. She is a recipient of the Stephen E. Dwornik Student Paper Award from the Geological Society of America (2001). She received a Ph.D. in Planetary Sciences from the University of California, Davis. She was a member of the Academies’ Mitigation Panel of the Committee to Review Near-Earth Object Surveys and Hazard Mitigation Strategies.

ELIZABETH P. TURTLE is a research scientist at the John Hopkins University Applied Physics Lab. Her research focus is using remote sensing observations and numerical geophysical models to study geological structures and their implications for the surfaces and interiors of the planets on which they formed, including, impact cratering and tectonics on terrestrial planets and outer planet icy satellites, mountain formation on Io, creep of ice-rich permafrost on Mars, and lakes on Titan. She is the PI of the Europa Imaging System (EIS) for NASA's upcoming Europa mission, an associate of the Cassini Imaging Science Subsystem (ISS) and RADAR teams, and a Co-I of the Lunar Reconnaissance Orbiter Camera (LROC). Previously, Dr. Turtle was an assistant research scientist at the University of Arizona in the Department of Planetary Sciences. She earned her Ph.D. in planetary sciences from the University of Arizona, Tucson. She served as a member of the Satellites Panel for the Planetary Science Decadal Survey and as a member of the Committee on New Opportunities in Solar System Exploration.

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